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Thread: 3 different power sources

  1. #1
    Junior Member
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    3 different power sources

    Hi

    I have a question regarding power :
    I am building a MIDI controller and I want to connect it in 3 different ways : USB, MIDI and Ethernet
    My idea is to use a Teensy and a Bome Box, which has Power Over Ethernet.

    I will have 3 different options to power the Teensy :
    - from the USB when connected to the Bome Box's POE
    - from the USB itself when no Ethernet cable is connected to the Bome Box
    - from an external power supply (9V lowered to 5V)


    how can I implement that and make sure I am not going to damage the Teensy ?

  2. #2
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    Quote Originally Posted by peeddrroo View Post
    Hi

    I have a question regarding power :
    I am building a MIDI controller and I want to connect it in 3 different ways : USB, MIDI and Ethernet
    My idea is to use a Teensy and a Bome Box, which has Power Over Ethernet.

    I will have 3 different options to power the Teensy :
    - from the USB when connected to the Bome Box's POE
    - from the USB itself when no Ethernet cable is connected to the Bome Box
    - from an external power supply (9V lowered to 5V)


    how can I implement that and make sure I am not going to damage the Teensy ?
    Which Teensy?
    Are you making a pcb?

  3. #3
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    I plan on using a Teensy LC as I need 5V output for LEDs.
    Yes, I'm making a PCB.
    I have drawn a little sketch of the connections.
    The red lines show cables providing power.

    The 9v power supply won't always be connected, neither will the ethernet or the USB, so I need to provide power with any of those.
    The 2 USBs won't be connected at the same time.

    I guess my question comes down to : Is there a way to provide power to the Teensy via an external source and still be able to power it with the USB without using a switch ?
    Click image for larger version. 

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  4. #4
    Senior Member BriComp's Avatar
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    I plan on using a Teensy LC as I need 5V output for LEDs.
    You realise that the LC is NOT 5V tolerant.

  5. #5
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    Quote Originally Posted by BriComp View Post
    You realise that the LC is NOT 5V tolerant.
    Pin 17 is at VIn voltage so it can provide 5V.

  6. #6
    Senior Member PaulStoffregen's Avatar
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    Quote Originally Posted by peeddrroo View Post
    I guess my question comes down to : Is there a way to provide power to the Teensy via an external source and still be able to power it with the USB without using a switch ?
    You could cut the VUSB-VIN pads apart. Then on your PCB, connect a diode from VUSB to VIN(5V). And from your 5V regulator (Teensy LC can't run directly from 9V) use another diode from regulator output to VIN.


    Quote Originally Posted by BriComp View Post
    You realise that the LC is NOT 5V tolerant.
    The normal pins aren't 5V outputs or 5V tolerant, but the special output connected to pin 17 is a 5 volt buffered output.

    But the buffer chip is powered by the VIN pin. If VIN has diodes between it and the actual 5V power, it will probably get about 4.3V with normal diodes or 4.5V with schottky diodes. Maybe that's still ok for the LEDs?

  7. #7
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    Thanks a lot Paul, that helps.

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